Here's a snagged screen pointing to video recording and playback coming to the Sidekick LX in a future update. Nothing definitive on which codecs will be supported, but possibly H.264, which YouTube encodes videos in for Apple, meaning you might be able to watch YouTube videos. Or it could be a different one, and there's no word on whether there'll be a dedicated YouTube app. Regardless, video capabilities of some kind seem to be in the pipe. [Hiptop3]
that just looks like a theme to me. i had a sidekick 3 for a year and a half and the only real tinkering i found to be able to do was make themes.
with a developer key however (going to danger, writing a small app, and getting approved) you could run your own code on the device, otherwise you were stuck with the catalog of stuff or what was already on there.